This invention relates to turf landscape irrigation systems and, more particularly, to underground, automatically timed irrigation systems which utilize pop-up fixed spray heads to distribute water.
Installed sprinkler irrigation systems generally fall into two broad categories, spray head sprinklers and rotary sprinklers. Spray head sprinklers, once turned on with water flowing through a piping system, pop-up to a height (2-6 inches typically) and become fixed, spraying out water in a pattern of a full circle, half circle, quarter circle or any required arc segment of a full circle with a range radius of 0 to 17 feet. Rotary sprinklers, on the other hand, once turned on with water flowing through a piping system, pop-up to a height (2-6 inches typically) and throw a relatively thin stream out to a determined radius (typically 20 to 50 feet) while rotating through a circle or partial circle to be irrigated. The rotation of a rotary head is typically accomplished by utilizing the energy of the pressurized water stream moving through the rotary head and out the nozzle in the stream. The water moves a series of vanes which drive a gear train to produce the desired rotational motion. Variations of rotary sprinkler heads exist with different mechanisms to extract the energy of the flowing stream to cause rotation, i.e. a ball striking a plate within a swirling stream, a spring-loaded arm entering a high energy stream, etc.
Rotary sprinklers are found to have certain advantages over pop-up spray head sprinklers. First, they have a lighter precipitation rate, or rate of water application, which is better suited to the intake rate of most soils and turf combinations. This lighter precipitation rate means less water running off of the turf and smaller pipes per equivalent irrigated area. The lighter precipitation rate also is less taxing to municipal water systems, which must design water treatment and pumping facilities to handle the maximum load of irrigation systems which are turned on, almost simultaneously, in the summer months. The second observed advantage or rotary irrigation systems is more uniform water distribution to the irrigated turf area.
One test which is conducted to determine the uniformity of an irrigation sprinkler head is termed a "catch can" test. In this test, a series of cans are spaced about the head while it is running, catching the water at the different locations about the head. Through measurement of the amount of water caught, the uniformity of the particular head can be determined.
One measure of this testing is termed the "scheduling coefficient" of the head, which is basically a multiplier times the required water application for the plant material to ensure that all areas serviced by the sprinkler head receive the required water. For instance, if a particular sprinkler head had a measured scheduling coefficient of 1.8, then 1.8 times the required water would have to be put out to ensure that all areas would receive the required amount. Obviously, at 1.8 times the required water, if some areas are just receiving the required amount, others are being greatly over watered. Using the scheduling coefficient as a uniformity measure, a coefficient of 1.0 would be a perfectly uniform sprinkler and any amount over 1.0 would represent the non-uniformity of the system. Most rotary heads have scheduling coefficience in the range of 1.2 to 1.5. The relatively efficient application of water of the rotary heads can be attributed to the fact that the single water stream is rotated through the arc slowly, and it is much easier to obtain an even fallout of a single stream as opposed to a fanned-out spray head pattern.
Pop-up spray heads have advantages over rotary heads and are predominantly utilized in residential and light commercial applications because of their small wetted radius (0 to 17 feet) which is easy to fit into small irregularly shaped lawns typical of these type of installations. The disadvantages that spray heads have against rotors are a higher precipitation rate (typically 1.2 to 1.5 inches per hour which is a much higher application of water than can be absorbed by the turf, leading to excessive runoff and waste of water) and a less uniform wetting pattern with a scheduling coefficient that typically ranges from 1.5 up to 3.0.
The primary reason for the non-uniformity of pop-up spray heads can be found in the spray pattern itself. A spray head must take a fixed flow of water and attempt to evenly distribute the water around the head in a certain arc and radius through a series of water droplets. All of the water starts from the same source within the head at the same pressure. In order to get the water droplets to distribute uniformly around the head, they must be of different mass and size. For a droplet to have enough kinetic energy to make it to the outer limits of the wetting pattern, it must have considerable mass. On the opposite end of the spectrum, for a droplet to fall close to the spray head, it must have kinetic energy and small mass. The problem is that small droplets with small kinetic energy and small mass that will drop out close to the head in perfect conditions will drift great distances with any minimal wind condition. Very rarely do perfect conditions exist when the spray head is operating and the effect of the head itself creates wind conditions. The non-uniformity and high precipitation rate have led to a widespread search for a more efficient means to irrigate turf areas associated with residential and light commercial areas.
Attempts to solve the problem with fixed pop-up sprinkler heads have included utilizing a secondary orifice to throw water close to the head. Larger droplets are "thrown" from the secondary nozzle to a close-in position via trajectory independent of kinetic energy of the droplets. This and other methods help improve the distribution uniformity but are expensive to implement. There exists no method to reduce the precipitation rate. No one method of improving the distribution uniformity and reducing the precipitation rate has been developed which is both effective and economical.